After a long run, water alone does not fully replace what sweat removed. Sodium is the main loss, and replacing fluid without it can leave you feeling no better than when you finished. The practical version is simple: drink to comfortable thirst, eat something with salt in it, and reserve deliberate electrolyte planning for genuinely long or hot efforts.
What sweat actually contains
Sweat is mostly water, with sodium the dominant electrolyte by a wide margin and smaller amounts of potassium, chloride and magnesium. Concentrations vary hugely between people — a salty sweater can lose two or three times what another runner loses over the same hour in the same conditions.
That variability is why fixed hourly sodium numbers work poorly. Two runners on the same route have genuinely different requirements, and the only reliable way to know yours is to measure it.
Why plain water sometimes is not enough
Drinking large volumes of plain water after heavy sweating dilutes what is left in the blood. Thirst can settle before fluid balance has actually been restored, which is why people finish a long run, drink steadily, and still feel flat, headachey or slightly nauseous.
In extreme cases — very long efforts with heavy plain-water intake — sodium can fall low enough to be genuinely dangerous. That is uncommon in everyday training, but it is the reason the advice is "drink to thirst" rather than "drink as much as possible".
Estimating your own losses
Weigh yourself before and after a long run, in similar clothing, and account for anything you drank. Each kilogram lost is roughly a litre of fluid. Do this on three or four different days and you will have a far better plan than any generic chart.
The visible version is simpler: if your kit has white salt marks, or if your skin tastes salty after a summer run, you are on the higher-loss end and should be more deliberate about replacement.
Rehydrating in practice
In the couple of hours after finishing, drink to thirst and eat normally. A meal with some salt in it does most of the work that a dedicated product would. If you are not eating soon, a drink containing sodium is more useful than the same volume of plain water.
You do not need to replace every gram lost immediately. For the large majority of training runs, normal eating and drinking across the rest of the day closes the gap. Deliberate strategies matter when you have another hard session within a day or so.
Sodium from food, not only from sachets
Ordinary food is a perfectly good sodium source: bread, cheese, soup, olives, salted nuts, a sandwich after the run. Most runners eating regular meals do not need an electrolyte product for a sixty-minute run, and the money is better spent on food they actually enjoy.
Products earn their place on long efforts in the heat, on back-to-back hard days, or when you genuinely cannot eat afterwards. They are a logistics tool, not a daily requirement.
Heat, humidity and the long-run plan
Hot and humid conditions raise sweat rate substantially and change the plan: carry fluid, start the run well hydrated rather than catching up mid-session, and accept a slower pace. Acclimatisation takes roughly a week or two, and the first hot week of the year is always the hardest.
Cold weather is the opposite trap — thirst blunts, and people under-drink because nothing reminds them. The weigh-in check catches this too.
What to carry, and what to leave at home
For runs up to about an hour, most people need nothing at all beyond a drink afterwards. Between one and two hours, carrying fluid becomes worthwhile in warm conditions, and a small amount of sodium helps if you are a heavy sweater.
Beyond two hours, or on hot days at any distance, plan it: fluid you can actually carry, sodium from a drink or food, and a route with known water. What you can leave at home is the elaborate protocol — most runners over-engineer hydration for sessions that never needed it.
Key takeaways
- Sweat is mostly water with sodium as the dominant electrolyte; losses vary two- to three-fold between runners.
- Drink to thirst rather than to a number; eating something salty does much of the replacement work.
- Weigh yourself before and after a long run — a kilogram lost is roughly a litre of fluid.
- Ordinary food covers sodium for most training runs; products suit long, hot or back-to-back efforts.
- Heat raises sweat rate and cold blunts thirst; adjust for both.
Frequently asked questions
Do I need electrolytes for a 10k?
For most people, no — normal food and fluid across the day cover it. They become worth planning for at longer distances, in heat, or when you sweat heavily.
How much should I drink during a long run?
Drinking to thirst is a sound default and avoids both dehydration and over-drinking. If you have measured your sweat rate, you can be more precise; if you have not, thirst is the better guide.
Are sports drinks the only option for sodium?
No. A sandwich, a bowl of soup or salted nuts after the run supply sodium alongside everything else in the food. Drinks are convenient when you cannot eat, not superior when you can.
What are the signs I have over-drunk?
Feeling bloated, nauseous or headachy despite drinking steadily, and needing to urinate frequently and copiously. If symptoms are significant after a long event, seek medical advice rather than drinking more.
Related supplements
If you want to explore this area, the Magnesium and Energy Support collections cover the relevant supplements and formats.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Talk to a healthcare professional before starting any new supplement, especially if you are pregnant, nursing, taking medication, or managing a health condition.